World's Oldest Shark Fossil Found

"I think it's an important discovery, one that raises and answers questions about ancient sharks," said Robert Purdy, a collection curator and paleontologist who studies early sharks at the Smithsonian Institution's National Museum of Natural History in Washington, D.C.

One of the fossil's most intriguing aspects is the large, paired spines on the shark's pectoral fins, the side fins used for steering. The feature was previously unknown in sharks and other chondrichthyans, an order of fish whose modern descendants include sharks, skates, rays, and chimaeras.

Their presence suggests the feature appeared in a common ancestor of jawed vertebrates, or gnathostomes. They also muddy the taxonomy of acanthodians, another, less-understood fish order that has bedeviled the classification of Doliodus problematicus since the shark species was first described in 1892 by English paleontologist A. H. Woodward. (Woodward based his study on a single tooth collected at the same fossil site near Atholville, New Brunswick.)

Teeth found in the shark's upper and lower jaw were also "quiet exceptional," Cloutier said. Clustered three to four deep and arrayed in multiple shapes, the batteries resembled the whorls of self-replacing teeth found in modern sharks. Scientists were unaware that Devonian fish displayed such tooth-replacement adaptations.

The Age of Fish

Four hundred million years ago, the area we know today as the Canadian Maritimes lay south of the Equator on the edge of Euramerica, one of two large continents on Earth that would later separate to become North America and Europe.

Terrestrial animal life was limited to unwinged insects like millipedes and scorpions. There were no trees, flowers, reptiles, birds, or mammals. Vertebrates wouldn't crawl on land for another 90 million years. Most living organisms were found in the oceans, an almost phantasmagoric world filled with primitive species even more diverse than today's marine life.

Atholville, New Brunswick, lay underwater in a coastal estuary, a brackish fresh and salt water environment teeming with life. It was there that the Doliodus problematicus shark perished and was quickly buried in fine sediment, enabling fossilization to occur.

The specimen remained undisturbed until 1997, when Miller led a field expedition to the site. Student assistant Jeff McGovern discovered the shark embedded in an outcrop of a mudstone cliff.

Two months later, Cloutier, the Quebec paleontologist, found the counterpart to the shark's braincase lying exposed on the outcrop while on a fossil hunting trip for Devonian plants.

Only later, while comparing specimens, did Miller and Turner realize that the fossil specimen came not only from the same ancient shark species, but from the same individual.

Researchers say their next steps are to more fully describe the fossil and to analyze the shark's compressed braincase under a CAT scan at a laboratory at the University of Texas in Austin that specializes in imaging paleo-objects.

Miller said he also hopes to study the relationship, if any, between Doliodus problematicus and giant, ancient sea scorpions, a type of eurypterid related to horseshoe crabs. A contemporary of Doliodus, the creature grew up to two meters long (6.5 feet) and bore a vague resemblance to a scorpion or lobster.

"Imagine a lobster standing on its tail that's as tall as you are," he said.